''Order my steps in your word, dear Lord,'' their voices surge, repeating one of contemporary gospel's popular hymns. ''Guide my feet in your word. Show me how to walk in your word.''

Johnson smiles down at the tiny $20 plastic monitor clipped to her skirt. ''31,995,'' the pedometer reads, documenting the number of steps she's taken in a week. Nearly 13 miles.

Johnson, 48, is one of 150,000 people in Colorado in a program determining whether modest physical effort will prevent weight gain now recognized as America's second-leading cause of preventable death behind smoking.

On Thursday, the pedometer program expands nationally. Hill hopes to have 1 million people signed up for ''America on the Move'' who will begin walking at least 2,500 steps a day, about a mile, to burn 100 calories.

And they'll trim another 100 calories a day from their diets. That's the equivalent of ordering a regular sack of french fries instead of supersizing.

Note: You can still have the fries. Just fewer of them.

Johnson, who directs health programs for the Metro Denver Black Church Initiative, started wearing a pedometer more than a year ago. She not only stopped gaining weight, but when she increased her daily walking to about 10,000 steps she lost more than a dozen pounds and cut back her hypertension medicine.

Now she considers the paths of health and redemption to be intertwined. ''It's the same as the gospel,'' she says. ''God doesn't care where you are when you start. You will reap the reward.''

For decades, physicians have known that tobacco causes lung cancer, emphysema and cardiovascular deaths. And while doctors universally recommend moderate exercise and a balanced diet, metabolism is so mysterious and people's habits so fickle that researchers cannot say precisely why some Americans are inflating while others aren't. Or, whether losing weight really will help anyone live longer.

Results from the Colorado walking effort are being submitted to scientific journals. Researchers studied more than 1,000 participants from populations as varied as urban black churches, a middle school, a smokestack city with a large Hispanic population, and ranching families in a High Plains town.

Over 16 weeks, 85 percent of all participants raised their activity level by at least 2,500 steps a day, the researchers say. But it will take a year to see if they stabilize, or even lose pounds, and it will take several years to see if the weight loss is sustained.

Like the Colorado experiment, only a fraction of America on the Move participants nationwide will be enrolled in a supervised study. Others can follow the same recommendations independently by registering on the program's Web site, individually or in a group. The self-reported data will be analyzed regularly, too.

James Hill, the program's co-founder, says it's the first effort at systematically studying ''how you stop obesity from getting worse.''

''Our idea is dirt simple,'' says Hill, director of the Center for Human Nutrition at the University of Colorado Health Sciences Center. ''The mistake we've made in weight-loss programs is telling people they need to change too much. The step counter gives you credit for what you're already doing.''

Hill is seeking a community that he can evaluate over many years akin to the landmark Framingham, Mass., heart study, which has been tracking residents since 1948. In fact, some previous obesity health data came from that Boston suburb.

A big difference, he acknowledges, is that when the Framingham project was launched, researchers didn't know the risks of jelly doughnuts for breakfast, or cigarettes. It was decades before they began recommending aggressive treatment of high blood pressure and high cholesterol, as well as changing risky behaviors.

Hill is encouraging people to change now rather than wait for new data. Speaking in superlatives rarely uttered in a lab, he enthusiastically speaks of America on the Move becoming ''a social movement.''

''If it doesn't work,'' he says, ''we're in big trouble as a nation.''

Two out of three adult Americans are overweight, the government says, and they're gaining nearly 2 pounds every year. A quarter of them get virtually no exercise.

Among children, 15 percent are too fat. Children as young as 6 are being diagnosed with type 2 diabetes commonly associated with adults.

For African-Americans, the problem of expanding waistlines is grimmer still; 60 percent of black men and 77 percent of black women are too heavy, doubling their already-elevated risk of diabetes and other diseases.

Regardless of who you are, probably 100 genes control your metabolism, the complex system that converts food into fuel for cells, burning some and storing the rest for later.

It's a system that emerged with the rise of mammals 65 million years ago and evolved in modern humans tens of thousands of years ago.

Its message to our upright-walking ancestors was to eat whenever they found food. They foraged for every precious calorie. (If you think the forest is nature's supermarket, just look at how reality TV show contestants look after a month in the wild. There's a reason the program is called ''Survivor.'')

Even after World War II, many of our grandparents still were hauling water and supplementing their emerging grocery store diets with vegetable gardens and small game. Their children walked to school and did chores.

Now food always is available. And it's not roots, berries and bugs. It's chips and dip. Burgers and fries. Pizza and beer.

Kids play video games. Segway, the hottest new gadget, is an upright scooter that eliminates the simplest stroll to the mailbox.

''Our bodies have never had to develop a system to avoid weight gain,'' said Hill, who walks 11,000 steps a day, about 4 1/2 miles. ''We have genes to tell us to rest, but we probably don't have a gene to tell us to be more active.''

Trial lawyers are suing Big Food the way they went after Big Tobacco. But Hill doesn't pin all the blame on restaurants and snack-makers. Technology, perversely, has boosted inactivity along with productivity. Hill says some obese people walk just a few hundred steps a day.

''They're going from bed to the car to the elevator to the desk and then back to the TV,'' he said.

''Over a decade, you gain 20 pounds. Then 20 more. Bill Gates probably is as responsible as McDonald's.''

On the Move critics draw different conclusions. Obesity isn't the result of flabby willpower, they say.

Food-seeking is a basic animal behavior that is hard-wired deep in our genetic code.

Appetite might not be as automatic as breathing, but it is as potent as thirst and could be more compelling than sex. Willpower naturally shrivels when we are surrounded by enticing foods and our genes are commanding us to eat.

And if we do manage to shed a few pounds, the same genes drive us to retain fat again.

Geneticist Jeffery Friedman of Rockefeller University doesn't wonder why so many people today are fat. He wonders why anyone is thin.

''There is a basic biological framework that regulates weight,'' Friedman said. ''Why is it we don't question this basic drive in any other mammal, but we somehow imagine it is not equally relevant or powerful in ourselves?''

To Friedman, walking and dieting whittle the edges of the obesity problem. He believes the solution lies in manipulating hormones and other chemical cues controlling appetite.

Since the mid-1990s, Friedman and others have discovered three hormones related to metabolism and hunger management, besides the old warhorse insulin. And they're looking for more.

Future therapies would block production of these hormones, or biochemically control the brain's appetite center, known as the hypothalamus, by fiddling with its hormone receptors. However, early experiments on this have had mixed results Hill says most heavy people don't have an obvious metabolic disorder caused by genetic mutations.

For years, Lucille Johnson simply ate more than she burned off.

A single mother of two, she confused being busy with being physically active. ''You don't get a lot of steps in your car,'' she admitted.

Now she rises at 5 a.m. to walk before her daughters go to school. After recuperating from injuries in a December car wreck, she's adding dance classes to get back to 10,000 steps a day.

''Once I was chopping collard greens and my girls ran upstairs to find out what the racket was all about,'' she said. ''I was marching in place. Had to get my steps.''

As for those greens, Johnson first trimmed 100 calories by limiting fatty snacks like cookies and cheese. Now she is reformulating her favorite soul foods, eliminating lard, ham hocks and bacon drippings.

''So much of African-American culture revolves around celebrating with food,'' she said. ''In the slave days, we got the scraps. We made them into our recipes, but not all of that food is good for you.''

Her daughters, a high school freshman and a sixth-grader, are tall and willowy. She gave both girls step-counters in hopes they will regularly outwalk their mother and remain thin.